The present invention relates to a coated cutting tool comprising a body coated with a textured alpha-alumina (α-Al2O3) layer, the method of making and use of the same. The layer is grown by chemical vapour deposition (CVD) and the invention provides an oxide layer with excellent wear properties and good performance in chip forming machining.
Typically, CVD alumina based coatings consist of an inner layer of titanium carbonitride and an outer layer of α-Al2O3. About 15 years ago it was found that further improvements of the alumina layer were possible by controlling the crystallographic orientation of the layer (texture). This was possible by the development of new synthesis routes comprising the use of nucleation and growth sequences, bonding layers, sequencing of the reactant gases, addition of texture modifying agents and/or by using alumina conversion layers. Commonly, the texture is evaluated by the use of X-ray diffraction (XRD) techniques and the concept of texture coefficients.
Textured Alumina Layer Synthesis Using Various Bonding/Nucleation Layers and Growth Sequences
U.S. Pat. No. 7,094,447 discloses a method to produce textured α-Al2O3 layers with improved wear resistance and toughness. The α-Al2O3 layer is formed on a (Ti,Al)(C,O,N) bonding layer using a nucleation sequence composed of aluminizing and oxidization steps. The layer is characterized by a strong {012} growth texture as determined by XRD.
U.S. Pat. No. 7,442,431 discloses a method to produce textured α-Al2O3 layers on a (Ti,Al)(C,O,N) bonding layer using a nucleation sequence composed of short pulses and purges of Ti-containing pulses and oxidizing pulses. The layer is characterized by a strong {110} growth texture as determined by XRD.
U.S. Pat. No. 7,455,900 discloses a method to produce textured α-Al2O3 layers on a (Ti,Al)(C,O,N) bonding layer using a nucleation sequence composed of short pulses and purges consisting of Ti+Al pulses and oxidizing pulses. The layer is characterized by a strong {116} growth texture as determined by XRD.
U.S. Pat. No. 7,442,432 discloses a method to produce textured α-Al2O3 layers on a (Ti,Al)(C,O,N) bonding layer with a modified but similar technique as disclosed in U.S. Pat. No. 7,455,900. The layer is characterized by a strong {104} growth texture as determined by XRD.
US 2007104945 discloses a textured α-Al2O3 coated cutting tool insert for which a nucleation controlled, α-Al2O3 layer texture is obtained. The layer is characterized by a strong {006} growth texture as determined by XRD.
US 2008187774 discloses a texture-hardened α-Al2O3 coated cutting tool insert with a {006} growth texture as determined by XRD.
U.S. Pat. No. 6,333,103 discloses a textured α-Al2O3 layer grown on a TiCO bonding layer characterized by a {1010} growth texture as determined by XRD.
Textured Alumina Layer Synthesis Using Sequencing of Reactant Gases
U.S. Pat. No. 5,654,035 discloses a body coated with refractory single- or multilayers, wherein specific layers are characterized by a controlled microstructure and phase composition with crystal planes grown in a preferential direction with respect to the surface of the coated body (growth texture). The textured α-Al2O3 layer is obtained by sequencing of the reactant gases in the following order: CO2, CO and AlCl3. The layer is characterized by a strong {012} growth texture as determined by XRD.
U.S. Pat. No. 5,766,782 discloses a cutting tool coated with refractory single- or multilayers including α-Al2O3, wherein specific layers are characterized by a controlled growth texture with respect to the surface of the coated body. The textured α-Al2O3 layer is obtained by sequencing of the reactant gases such that first CO2 and CO are supplied to the reactor in an N2 and/or Ar atmosphere followed by supplying H2 and AlCl3 to the reactor. The layer is characterized by a {104} growth texture as determined by XRD.
Textured Alumina Layer Synthesis Using Texture Modifying Agents
U.S. Pat. No. 7,011,867 discloses a coated cutting tool comprising one or more layers of refractory compounds out of which at least one layer is an α-Al2O3 layer having a columnar grain-structure and a strong {300} growth texture as determined by XRD. The microstructure and texture is obtained by adding ZrCl4 as a texture modifying agent to the reaction gas during growth.
U.S. Pat. No. 5,980,988 discloses a {110} textured α-Al2O3 layer as obtained by using SF6 as a texture modifying agent during growth. The texture is determined by XRD.
U.S. Pat. No. 5,702,808 discloses a {110} textured α-Al2O3 layer as obtained sequencing SF6 and H2S during growth. The texture is determined by XRD.
Textured Alumina Layer Synthesis Using Conversion Layers
U.S. RE41111 discloses a {001} textured α-Al2O3 layer as obtained using an initial heat treated alumina core layer (conversion layer) with a thickness of 20-200 nm. The texture is determined by electron back scattering diffraction (EBSD).
An explanation of EBSD and the analysis for texture evaluation by using pole figures, pole plots, orientation distribution functions (ODFs) and texture indexes can for instance be found in Introduction to Texture Analysis: Macrotexture, Microtexture, and Orientation Mapping, Valerie Randle and Olaf Engler, (ISBN 90-5699-224-4) pp. 13-40.
Typically, the evaluation of texture may comprise                i) construction of the ODF,        ii) identifying the components Euler angles φ1, Φ and φ2 (cf. FIG. 1) and their corresponding ODF densities and texture indexes,        iii) construction of pole figure(s) of relevant texture components and        iv) construction of pole plot(s) of the relevant texture components.        